Biochar type and application methods affected nitrogen and phosphorus leaching from a sandy soil amended with inorganic fertilizers and biosolids

Land application of biochar as a soil amendment can be an effective strategy for reducing nutrient leaching while providing simultaneous benefits to soil health. However, biochar effects on soil nitrogen (N) and phosphorus (P) dynamics in biochar-amended soils are poorly understood, particularly in Florida sandy soils receiving fertilizers. This study evaluated the effects of different biochar materials (particle size of 0.1 mm produced from pine (Pinus spp.) wood vs. similar to 0.5-2 mm produced from fescue (Festuca arundinaceaSchreb.) grass, herein referred as powder and coarse biochar, respectively) and their application methods (surface vs. incorporated) on N and P leaching from soils amended with inorganic fertilizer or biosolids. Biochar materials were either mixed throughout columns of soil or surface applied at a 1% (w/w) rate. Columns were periodically leached over 6 mo to attain 138 ml (equivalent to similar to 1 pore volume) of drainage in each event (total of similar to 16 pore volume of leachate). Biochar materials exhibited modest affinity to retain ammonium (NH4+) but showed no ability to sorb nitrate (NO3-). Powder biochar incorporated throughout the soil reduced cumulative NH4-N, NO3-N, and total N mass leached (average of 25% reduction) relative to control (no biochar) treatments. Biochar materials acted as P sources and were ineffective in reducing leachate P. Biosolids generally resulted in significant lower risk of N and P leaching than inorganic fertilizer. Results suggested biochar ability to retain N and P in soils varies with biochar source, application method, and nutrient source. Biochar type and application method affected N and P dynamics in biosolids or inorganic fertilizer-amended soils, but understanding the mechanisms requires additional study.

Automated summary

Land application of biochar as a soil amendment can help reduce nutrient leaching and improve soil health. However, the effects of biochar on nitrogen and phosphorus dynamics in sandy soils receiving fertilizers are not well understood. This study found that biochar materials had some ability to retain ammonium but not nitrate, and acted as a source of phosphorus. Applying biosolids instead of inorganic fertilizers resulted in lower leaching risks for nitrogen and phosphorus. The results highlighted the importance of understanding the source and application method of biochar in influencing nitrogen and phosphorus dynamics.